Born in Thornaby-on-Tees, North Yorkshire, in the North-east of England, Marlene Sidaway originally trained as an adding-machine operator when she left school, but in 1961 she left for London to join a childrens' theatre group and studied acting at the East 15 acting school. Although she has been a familiar character player on television since the 1970s she is also the secretary of the International Brigade Society, commemorating the volunteers who enlisted to fight Fascism in the Spanish Civil War, Marlene's much older partner, David Marshall, having been a member of the Brigade. They lived together from 1990 until his death in 2005.